We used to say that three big swing states are crucial: Ohio, Florida, and Pennsylvania. Whoever wins two out of the three wins the White House. Given this year’s electoral map, I think that Trump must pretty much run the table on all three. Pennsylvania, on the other hand, is close to a must win for Joe Biden.
Florida and North Carolina will be good and early indicators of how the night will go. If they are called for Biden, Trump is in deep trouble. In any case, I suggest being careful with the exit polls. They have been wrong in the past (2004, 2016) and might be wrong again. This being said, we might actually not know by the end of the night who the next president will be. If the results are close, we might not even know for days or even weeks.